For VDD = 1.8 V and using IREF = 100 muA. it is required to design the circuit o

Question

For VDD = 1.8 V and using IREF = 100 muA. it is required to design the circuit of Fig. 7.22 to obtain an output current whose nominal value is 100 muA. Find R if Q1, and Q2 are matched with channel lengths of 0.5 mum, channel widths of 4 mum. Vt = 0.5 V, and k'n = 400 muA/V2. What is the lowest possible value of Vo? Assuming that for this process technology the Early voltage V'A = 10V/mum. find the output resistance of the current source. Also, find the change in output current resulting from a +0.5-V change in V0.

Explanation / Answer

VDD=1.8 V, Io=Iref=100 A, L=0.5 m, W=4 m, V'A=10 V/m, Vt=0.5 V

kn=400 A/V2, Io=ID=1/2*kn*(W/L)*V2OV, VOV=(2*ID/(kn*(W/L)))0.25 V

VDS=VGS=Vt+VOV=0.75 V

R=(1.8-0.75)/0.000110,500

VDS2=VOV=0.25 V

Ro=ro=VA*L/ID50,000

IDVo/ro=0.5/50000=0.00001 A

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